The present invention relates generally to a dot line printer, and more particularly to an ink ribbon guide for enhancing a running stability of an ink ribbon.
Referring to FIG. 1, an arrangement of a conventional dot line printer will be described. The dot line printer includes a hammer mechanism provided with a hammer bank 10. The hammer bank 10 is reciprocally movable along a line extending in a direction transverse with respect to a print paper. The hammer bank 10 accommodates a plurality of print hammers 11 which perform printing on the print paper on a dot line basis as the hammer bank 10 reciprocates back and forth.
There have been several mechanism proposed for reciprocally moving the hammer bank 10. A typical mechanism uses a cam or a ball screw with which a rotational motion produced by a motor is translated into a reciprocal linear motion. Another mechanism uses a voice coil motor or a linear motor with which the hammer bank 10 is directly moved reciprocally. Of those, the cam mechanism and the drive arrangement using the voice coil motor are suitable for a higher repetitive frequency of the reciprocal motion. On the other hand, the mechanisms using the ball screw and the linear motor is suitable for a lower repetitive frequency of the reciprocal motion. The cam mechanism or the voice coil motor is typically provided in one side portion of a hammer bank 10 in terms of facility, reliability and constraint in joining the hammer bank 10 and a hammer bank shuttle mechanism 20. (The shuttle mechanism 20 is known as a mechanism for reciprocating the hammer bank 10.) An arrangement of the dot line printer using the cam mechanism as the shuttling means, a printing scheme, and potential problems involved will be described.
The shuttle mechanism 20 is disposed in one side of the hammer bank 10 (right side in FIG. 1), and is coupled to the hammer bank 10 with a bolt 21. This arrangement is disclosed in U.S. Pat. No. 4,889,052. The shuttle mechanism 20 includes a cam 22 rotatable by a shuttle motor (not shown), a pair of cam followers 23 provided in rolling contact with the cam 22, a shiftable plate 24 and a shiftable shaft 25. Upon rotation of the cam 22, the shiftable plate 24 and the shiftable shaft 25 are reciprocally movable in an axial direction of the shaft 25 through the cam followers 23. For supporting and guiding the shiftable shaft 25, linear bearings 26 are provided. The shiftable shaft 25 extends through the bearing 26 and is coupled to the hammer bank 10 by the bolt 21.
A bank shaft 27 is connected to another side of the hammer bank 10 (left side in FIG. 1), and another linear bearing 28 is provided for supporting the bank shaft 27, to thereby support the reciprocal motion of the hammer bank 10. Print hammers 11 are arranged in spaced apart relation to one another in the direction in which the hammer bank 10 moves. Although not shown, a print hammer driver is provided in association with each print hammer 11, which includes a permanent magnet, a yoke and a release coil. The hammer 11 is attracted to the face of the yoke pole by the permanent magnet and is released therefrom in response to the energization of the release coil, whereby the dot pin strikes the paper through an ink ribbon 40 to thus make an impression of a dot on a paper 30.
A platen 31 is provided on a sheet feed mechanism which includes a paper feed motor (not shown). The sheet feed mechanism is adapted to feed a print paper in a direction perpendicular to a reciprocating direction of the hammer bank 10. The platen 31 is positioned slightly spaced away from the hammer bank 10 for bearing dot impression force applied from the print hammers 11 and for guiding travel of the paper 30. Both end portions of the platen 31 are rotatably supported by hearings 32 coupled to a sheet feed frame 33 of the sheet feed mechanism. Incidentally, the sheet feed mechanism also includes a tractor (not shown) positioned above the platen 31. The print paper is engageable with the tractor in a known manner.
Between the hammer bank 10 and the platen 31, the ink ribbon 40 is positioned. Further, a pair of ribbon guides 41 and 42 are provided for defining an ink ribbon path along which the ink ribbon 40 travels in a direction indicated by an arrow at a predetermined speed. One of the ribbon guides 41 is positioned at a left side of the hammer bank 10, while the other ribbon guide 42 is positioned at a right side of the shuttle mechanism 20. The ink ribbon 40 is of an elongated tape like configuration and has a width ranging from 0.5 to 1.5 inches and a length ranging from 50 to 100 m. The ink ribbon 40 is formed of a nylon impregnated with an ink.
An ink ribbon cassette 45 is detachably provided at a given location for accommodating therein the ink ribbon 40. The cassette 45 is formed with an ink ribbon outlet at which a ribbon brake means 46 is provided so as to impart a proper tension to the ink ribbon 40. Further, the cassette 45 is formed with an ink ribbon inlet portion at which a pair of drive rollers 43 are provided to drivingly feed the ink ribbon 40. Furthermore, an ink ribbon sensor 44 is provided for detecting malfunction in running the ink ribbon 40. The ink ribbon sensor 44 also serves as a guide means for guiding travel of the ink ribbon 40. With the structure, the ink ribbon 40 accommodated in the cassette 45 is discharged through the ribbon brake means 46, and runs in parallel with the platen 31 by the guidance of the ink ribbon guides 41 and 42, and is pulled into the cassette 45 by the drive rollers 43 through the ink ribbon sensor 44. When the ink ribbon 40 is at a position between the ink ribbon guides 41 and 42, the ink ribbon 40 is apparently positioned between the hammer bank 10 and the platen 31.
With the above described structure, when the shuttle motor is energized, the hammer bank 10 shuttles back and forth along a print line. During the movement of the hammer bank 10 in the right-hand direction, the print hammers 11 are selectively fired, thereby making dot impressions on the paper 30. The hammer bank 10 reaches the rightmost position and turns around thereat. At this time, the paper feed motor (not shown) is energized to advance the paper 30. The hammer bank 10 then moves leftwardly and the print hammers 11 makes another dot impressions on the paper 30. In this manner, one line made up of plural dot lines is printed by repeatedly carrying out such alternate print and paper feed cycles.
In the case of the high speed dot impression process, printing is carried out at a speed of 300 lines per minute with 100 dots per character for 136 columnar characters per line. Therefore, the number of printed dots can be as many as 68,000 dots per second (300.times.100.times.136/60). Instantaneously, there may be a case where the number of the dots is not less than 100,000 dots per second. Further, various kinds of printing papers 30 may be loaded on the printer. Among these, relatively thick paper such as 5-fold to 8-fold carbonless duplicating papers or no carbon papers such as those used for multi-slips may also be loaded. In this case, edge portions of the multi-slips are pasted up or are joined together by a stapler. Therefore, locally thick portion may exist in the paper to be loaded in the dot printer. Furthermore, the paper 30 is fed at the lowest velocity of about 1 inch per second in the case where printing is done on a line by line basis. On the other hand, the paper feed velocity may be increased up to 15 to 25 inches per second in the case where printing jumps every several lines or requires a blank portion.